Chiral recognition by inclusion crystals of Amino-Acid derivatives having trityl groups

Abstract

Enantioselective inclusion of racemic guests into chiral hosts can be used for enantiomeric resolution. We propose new crystalline host designs consisting of amino-acid derivatives having trityl groups. We first show that an N,N0-ditrityl amino amide host includes N-phenyl-2-halobutanamides (halogens: Cl and Br) in the host cavity to form inclusion crystals with high enantioselectivities (82-83% ee, S-form).We then show that salts between N-trityl amino acids and tert-butylamine include several alcohols and that racemic 1-chloro-2-propanol is resolved to give the S-enriched sample of 69 % ee. In both of these kinds of hosts, trityl groups serve as crystal engineering tools for constructing inclusion crystals. The installation of trityl groups into amino-acid derivatives breaks their inherent hydrogen bonds, and the inclusion of guest molecules (amides or alcohols) compensates the loss of hydrogen bonds. Single-crystal X-ray analysis has elucidated these inclusion cavities and host-guest interactions.